The proposed research seeks to identify and characterize the system of brainstem neurons which mediates genital sensations in female cats. Animals will be ovariectomized and either anestrous or behaviorally estrous due to estradiol injections in order to examine the effects of the hormone on responses of genital sensory neurons. It has been shown in previous work that many neurons in the ventrolateral medulla are specifically responsive to vaginal probing, and that the response patterns of these cells as a group differ between estrous and anestrous cats. In the proposed work, the genital sensory system will be traced further rostrally, toward the diencephalon, by microelectrode recording. The brainstem neurons found to respond to vaginal probing will be studied in detail by single-unit recording in order to identify their response patterns, response specificity and to compare these patterns in units from estrous and anestrous cats. Preliminary work will be undertaken on recording of single-unit responses to vaginal stimulation from selected brainstem sites in waking, behaving cats. The results of the proposed investigations will provide a delineation of the ascending genital sensory system, and should serve as a neural model for understanding the modulation by estrogens of the cat's distinctive behavioral responses to vaginal stimulation.